Method for reinforcing steel pipe piling in situ and the resultant piling



Dec. 16, 1969 H. J. MEHEEN 3,483,707

METHOD FOR REINFORCING STEEL PIPE PILING IN SITU AND THE RESULTANT FILING Filed March ll, 1968 2 Sheets-Sheet 1 IN VEN TOR. HOM/f Yo a/v u. MEA/551V;

82mm, jm f 251mm/ Dec. 16. 1969 H. J. MEHEEN METHOD FOR REINFORCING STEEL PIPE FILING IN SITU AND THE RESULTANT PILING Filed March ll, 1968 2 Sheets-Sheet 2 IN VEN TOR. MEA/EEN,

HOMYOU/V d ATTOF/VEYS.

US. Cl. 61-46 7 Claims ABSTRACT OF THE DISCLOSURE Reinforcement for Steel pipe piles, such as those supporting off-shore oil platforms, which have deteriorated and lost their strength. The pile is reinforced in situ, by cutting an access opening into its interior and introducing a partially prestressed and partially reinforced concrete pile inside the steel shell.

This invention relates to a method for reinforcing steel pipe piling in situ and the resultant pile construction.

The method of this invention is particularly applicable to steel pipe piles in situ, such as those supporting offshore oil platforms. Because of wave and wind action, the steel piling is subject to substantial lateral stresses and high bending moments, continuously. Furthermore, after a period of time, the corrosive effect of the salt water surrounding the piles causes them to lose strength. The combination of these factors often results in buckling of the piles.

In order to restore the piling to its original strength, I introduce a partially prestressed and partially reinforced concrete pile inside each steel pipe pile, in situ. The resultant pile will have a much higher capacity to resist both vertical and lateral stresses, while resisting corrosion and deterioration.

Accordingly, it is an object of this invention to provide a method for reinforcing steel pipe piling, in situ, by introducing a partially prestressed and partially reinforced concrete pile inside of each steel pipe.

A further object of this invention is to provide an improved pile consisting of an outer steel shell, reinforced by an inner concrete pile which is free from cracking, is water-tight, and which can withstand high lateral stresses and bending moments.

Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

FIGURE 1 is a side -view in elevation of a steel pipe pile, partly in section, prior to being reinforced in accordance with the method of this invention;

FIGURE 2 is a side view in elevation similar to FIG- URE 1, partly in section, and illustrating an initial step in reinforcing the pile;

FIGURE 3 is a cross-sectional view taken substantially along the plane indicated by line 3-3 of FIGURE 2;

FIGURE 4 is a cross-sectional view taken substantially along the plane indicated by line 4-4 of FIGURE 3, and illustrating the finished, reinforced pile;

FIGURE 5 is a cross-sectional view taken substantially along the plane indicated by line 5 5 of FIGURE 3;

FIGURE 6 is a view similar to FIGURE 3, but illustrating an alternative method of reinforcing the pile;

FIGURE 7 is a cross-sectional view taken substantially along the plane indicated by line 7--7 of FIGURE 6;

FIGURE 8 is a cross-sectional view taken substantially along the plane indicated by line 8-8 of FIGURE 6; and

FIGURE 9 is an end view in elevation of a representative off-shore oil platform and support structure, and further illustrating the manner of practicing the invention.

nited States Patent ice Referring now to the drawings in detail, and particularly to FIGURES l to 5, and 9, a representative offshore oil platform construction is generally designated by the numeral 10. Platform 10 is supported above waterline 12, by a number of interconnected steel pipe piles 14. Piles 14 are anchored in the sea floor 16, and telescopically receive on their upper ends, sleeves 18. The platform 10 is supported on the top of sleeves 18 by beams 19. Each sleeve 18 serves as a cap for a pile 14, and is interconnected by bracing to space the piles.

In order to prepare each pile 14 for reinforcement in situ, a work platform 20 is suspended from platform 10. A substantially rectangular access opening 22 is cut through sleeve 18 and pile 14 to expose the interior of the pile. The opening 22 is cut as close to the top of the pile as possible, but no closer than one foot. The exterior of the pile 14 is reinforced adjacent opening 22 with stiffeners comprising angle irons 24 and 26, Welded to pile 14 on opposite sides of opening 22.

All mud, water, and other impurities are then removed from the interior of the pile to a depth which varies depending on the condition of pile 14 and the foundation material in sea floor 16. This can be accomplished by jetting and pumping. Once the pile is pumped to the desired depth, it should be plugged with mud or cement grout 28 so that no foreign matter will rise above this point. The pile 14 is now ready to be reinforced.

This invention contemplates reinforcing the piling by the introduction of concrete into the interior thereof through access opening 22. Concrete is moldable and readily flowable, and is an ideal structural support member for use as a support column in massive constructions, where the majority of the applied stresses are compressive. However, whenever a matetrial is subjected to compression in one direction, there lwill be an expansion in a direction perpendicular to the compression axis. The tensile and transverse strength of plain concrete is very low and unreliable, compared to its compressive strength, and, in order to make concrete available for use in columns which are subjected to bending moments and some tension, it is necessary to embed steel reinforcement in1 the concrete member. The purpose of the steel is to carry the exural and tensile stresses, and the union between the steel and concrete should be sufficient to make the two materials act as one.

In particular, the columns formed in this invention will have to withstand the application of direct horizontal forces Ibecause of wind and wave motion of the sea. An eccentric force of this nature will produce an even higher bending moment on the column than normal, and set up high flexural stresses. The maximum stress will occur on the side of the column and rapidly decrease towards its center. Therefore, the column formed herein should not only be reinforced, but the reinforcement should be as close to the perimeter of the column as possible, and symmetrically spaced.

Concrete expands as the temperature of its environment is raised and contracts as the temperature is lowered. Concrete will also expand in volume if kept wet or immersed in water and contract if exposed to air. This latter property is not confined to freshly placed concrete, but is characteristic of concrete of many years service This tendency to change in volume with different moisture conditions and changes in temperature does, of course, set up stresses of both tension and compression in a restrained reinforcedconcrete structure. The tensile stresses often exceed the `amount that the concrete can sustain, and cracks result. Also, when reinforced concrete structures are subjected to high exure, the concrete in the tensile zone will crack to .allow the reinforcing steel to carry the stresses. In order to overcome these stresses, the concrete should be placed under an additional, axial, compressive load, which will close the cracks after the lateral loads are removed.

I achieve these objectives by providing flexible-steel tendons housed in exible tubing within the concrete introduced into the steel pile. The tendons are supported between plates and are spread symmetrically as close to the perimeter of the steel pile as possible and stressed partially, just enough to introduce sucient compression in the concrete to render the concrete crack-free and watertight. The residual area of the stressed tendons 'will then act as normal reinforcing steel when the pile is subjected to high lateral forces, and consequently, high bending moments. If the tendons are stressed to their limit they will create excessive compression in the concrete, and the concrete would become incapable of resisting any further bending. The same tendons are used to establish an additional axial load in the concrete and for reinforcement A further vadvantage is obtained by using tlexible prestressed tendons. Because of their exibility, they can be placed easily through the small access hole and their high ultimate strength gives the piles their strength. As illustrated in FIGURES 2 to 5, eight symmetrically spaced, flexible steel tendons 30 housed in flexible tubing 49 are secured by conventional means to annular bearing plate 32 and lowered into the interior of steel pile 14 through access opening 22, and positioned close to the periphery of steel pile 14. The tendons are lowered to a point approximately one foot from mud or grout plug 28 and are spaced approximately nine inches from the bottom of access opening 22.

At their upper ends, each strand 31 of tendons 30, passes through conical guides 33 secured to an upper annular bearing plate 34, seated on brackets 40 welded to the interior of pile 14, The strands 31 of each tendon 30 pass through an opening in bearing plate 34, and are secured to a prestressing washer 39. Washers 39 are -commercially available, and are manufactured by The Prescon Corporation of Corpus Christi, Tex.

Lateral ties 36, spaced along the tendons, hold them in circumferential alignment during the construction, and also provide lateral restraint for the reinforcing for resisting diagonal tension in the concrete.

A high strength, non-shrinking, concrete or cement grout is then pumped through a central opening in plate 34, into the interior of steel pipe 14, until it reaches the underside of plate 34. The grout should be pumped into the pile in suitable lifts so as not to exceed the crushing strength of the tubing 49 and the bursting strength of the pile 14. After the grout has reached adequate strength to be stressed, washers 39 are each pulled and tendons 30 stressed to the prescribed partial stress, by conventional machinery suitable for this purpose. Shims 41 are then placed under washers 39, between the washers and plate 34 to maintain the stress in each tendon. The flexible tubing 49 surrounding each tendon 30 is then pumped full of grout through central openings in washers 39, in order to create a bond between the tendons and grout and allow the remainder of the strength of the steel tendons to be used as reinforcement.

The upper ends of the tendons 30 and plate 34 are then embedded in grout to protect them from corrosion. The portions of pile 14 and sleeve 18, removed to form the access opening 22, are welded back in place to complete the construction.

FIGURES 6 to 8 illustrate an alternative manner of reinforcing a steel pipe pile. Elements corresponding to those shown in FIGURES 1 to 5 and 9 are designated by primed numerals.

The method used for reinforcing pile 14 is substantially identical to that used to reinforce pile 14, except that four symmetrically spaced tendons 30', which act as pure prestressing tendons only and are sheathed with exible tubing 49', are secured to plate 32', and lowered into the interior of pile 14. A number of smaller size flexible strands 44, which act as pure reinforcing and induce no prestressing in the concrete, are also secured to plate 32 adjacent to its periphery. The strands 44 pass through openings in the bearing plate 34 seated on brackets 40. while tendons 30 pass through conical adapters 33' on the plate 34.

Six to eight feet of grout is poured into the bottom of pile 14 to anchor plate 32. Alternatively, brackets 46 can be welded to the interior of pile 14 above plate 32. to prevent plate 32 from being raised.

Strands 44 are then stretched nominally with a force or" about 1,00() pounds by means of a small hydraulic ram, to keep them taut, and anchored to plate 34. The anchorage comprises a split cone 50, having a gripping surface S2. Cone is placed about strand 44, as shown in FIG- URE 8. Split cone S0 is in sliding engagement with a conical bore S4 in an outer sleeve 56. A coil spring 58 is seated on cone `5() and is adapted to be compressed by a cap threaded into the upper end of sleeve 56. As spring 58 is compressed, it will force cone 50 downwardly in bore 54. This in turn will force the gripping surfaces 52 of the cone inwardly, to tightly clamp about the strand 44.

The tendons 30 are not stressed at this time. After tensioning of the strands, grout is pumped into the interior of pile 14', as described in connection with FIG- URES l to 5, up to the underside of plate 34. When the grout has reached proper strength, the four tendons 36 are stressed fully, in the same manner as in FIG- URES 1 to 5, and anchored to plate 34. The flexible tubing 49 surrounding tendons 30 is then grouted full. The brackets 40', plate 34', and the top of tendons 30 and strands 44 are then embedded in grout.

An oil-shore platform reinforced as described, has considerably more strength than it had prior to reinforcement. Since the partially prestressed and reinforced concrete pile, induced inside of the in situ steel pile is capable of resisting all the forces alone, the residual strength of steel piles will constitute added strength. Furthermore, the concrete inside of the steel pile will prevent local buckling of steel, and by this stiffening action will assist the steel pile to carry considerably more stress without failure. Therefore, any amount of strength left in the steel pile will be added as an additional safety factor.

While speciiic embodiments of my invention have been disclosed in the foregoing description, it will be understood that various modications within the spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitations be placed on the invention except as defined by the scope of the appended claims.

I claim:

1. A method for reinforcing in situ a hollow pile structure supported on the bed of a body of water and having its upper end extending above the surface of said body of water, comprising the steps of cutting an access opening through the wall of said pile structure at a location above said surface of the .body of water, introducing a plurality of longitudinally extending, symmetrically spaced, flexible members into the interior of said pile structure through said access opening and anchoring said members to extend adjacent the periphery of said pile structure, pouring concrete into the interior of said pile structure through said access opening while preventing said members from bonding to said concrete as it hardens, pulling at least some of said unbonded members an amount suicient to develop at least a partial stress therein after said concrete hardens, and then lbonding said stressed members to said concrete, whereby said hollow pile structure is strengthened by an inner concrete pile reinforced against stresses and bending moments and placed under compression along its longitudinal axis.

2. A method in accordance with claim 1, wherein said pulling of the unbonded members is in suicient force to engender only partial stress therein.

3. A method in accordance with claim 1, wherein said pulling of the unbonded members is of suicient force to engender full stress therein.

4. A method in accordance with claim 1, wherein said step of anchoring the exible members to the hollow pile structure is at the bottom portions of said members and wherein after development of at least a partial stress in some of said members the top portions of the stressed members are anchored in said hollow pile structure, and after said step of pouring concrete into the interior of said pile the remainder of said flexible members are pulled to develop a full stress therein after said concrete hardens, followed by bonding said fully stressed members to said concrete.

5. A method in accordance with claim 1 including the step of closing said access opening by resecuring the portion of said pipe pile removed to form said opening.

6. A method in accordance with claim 1, wherein said exible members are individually encased in flexible tubes before the members are introduced into the pile structure to prevent bonding to the concrete.

7. A method in accordance with claim 6, wherein said flexible members are secured to spaced annular plates-before the members are introduced into the pile structure.

References Cited UNITED STATES PATENTS 3,188,816 6/1965 Koch 61-54 X 3,213,629 10/1965 Manning 61--54 X 3,382,680 5/1968 Takano 61-56 JACOB SHAPIRO, Primary Examiner.

U.S. C1. XR. 

